Browsing by Subject "Mobile computing"

Now showing 1 - 15 of 15

Open Access
Adaptive schemes for location update generation in execution location-dependent continuous queries
(Elsevier Inc., 2006-04) Lam, Kam-Yiu; Ulusoy, Özgür
An important feature that is expected to be owned by today's mobile computing systems is the ability of processing location-dependent continuous queries on moving objects. The result of a location-dependent query depends on the current location of the mobile client which has generated the query as well as the locations of the moving objects on which the query has been issued. When a location-dependent query is specified to be continuous, the result of the query can continuously change. In order to provide accurate and timely query results to a client, the location of the client as well as the locations of moving objects in the system has to be closely monitored. Most of the location generation methods proposed in the literature aim to optimize utilization of the limited wireless bandwidth. The issues of correctness and timeliness of query results reported to clients have been largely ignored. In this paper, we propose an adaptive monitoring method (AMM) and a deadline-driven method (DDM) for managing the locations of moving objects. The aim of our methods is to generate location updates with the consideration of maintaining the correctness of query evaluation results without increasing location update workload. Extensive simulation experiments have been conducted to investigate the performance of the proposed methods as compared to a well-known location update generation method, the plain dead-reckoning (pdr). © 2005 Elsevier Inc. All rights reserved.
Open Access
An evaluation of transaction management issues in mobile real-time database systems
(1998-01) Kayan, Ersan
The integration of issues from real-time database systems and mobile computing systems is a new research area that aims to provide support for real-time requirements of database applications in a mobile computing environment. Due to certain constraints of a mobile computing environment, such as resource-poor mobile computers, low-bandwidth and unreliable wireless links, and mobility of users/computers, various research issues in traditional real-time database systems need to be reconsidered. In this thesis, we investigate some of these issues using a detailed simulation model of a mobile real-time database management system. We propose a transaction execution model with two alternative execution strategies and evaluate the performance of the system considering various mobile system characteristics. Performance results are provided in terms of the fraction of transaction that satisfy their deadlines.
Open Access
Association rules for supporting hoarding in mobile computing environments
(IEEE, 2000) Saygın, Yücel; Ulusoy, Özgür; Elmagarmid, A. K.
One of the features that a mobile computer should provide is disconnected operation which is performed by hoarding. The process of hoarding can be described as loading the data items needed in the future to the client cache prior to disconnection. Automated hoarding is the process of predicting the hoard set without any user intervention. In this paper, we describe an application independent and generic technique for determining what should be hoarded prior to disconnection. Our method utilizes association rules that are extracted by data mining techniques for determining the set of items that should be hoarded to a mobile computer prior to disconnection. The proposed method was implemented and tested on synthetic data to estimate its effectiveness. Performance experiments determined that the proposed rule-based methods are effective in improving the system performance in terms of the cache hit ratio of mobile clients especially for small cache sizes.
Open Access
A comparison of epidemic algorithms in wireless sensor networks
(Elsevier BV, 2006-08-21) Akdere, M.; Bilgin, C. C.; Gerdaneri, O.; Korpeoglu, I.; Ulusoy, O.; Çetintemel, U.
We consider the problem of reliable data dissemination in the context of wireless sensor networks. For some application scenarios, reliable data dissemination to all nodes is necessary for propagating code updates, queries, and other sensitive information in wireless sensor networks. Epidemic algorithms are a natural approach for reliable distribution of information in such ad hoc, decentralized, and dynamic environments. In this paper we show the applicability of epidemic algorithms in the context of wireless sensor environments, and provide a comparative performance analysis of the three variants of epidemic algorithms in terms of message delivery rate, average message latency, and messaging overhead on the network. © 2006 Elsevier B.V. All rights reserved.
Open Access
A data mining approach for location prediction in mobile environments
(Elsevier, 2005) Yavaş G.; Katsaros, D.; Ulusoy, Özgür; Manolopoulos, Y.
Mobility prediction is one of the most essential issues that need to be explored for mobility management in mobile computing systems. In this paper, we propose a new algorithm for predicting the next inter-cell movement of a mobile user in a Personal Communication Systems network. In the first phase of our three-phase algorithm, user mobility patterns are mined from the history of mobile user trajectories. In the second phase, mobility rules are extracted from these patterns, and in the last phase, mobility predictions are accomplished by using these rules. The performance of the proposed algorithm is evaluated through simulation as compared to two other prediction methods. The performance results obtained in terms of Precision and Recall indicate that our method can make more accurate predictions than the other methods. © 2004 Elsevier B.V. All rights reserved.
Open Access
Dikgen frekans bölmeli çoklu erişim sistemlerinde telsiz erişim terminallerinin işbirliği
(IEEE, 2009-04) Tokel, Turgut Barış; Aktaş, Defne
Gelecek nesil kablosuz iletişim sistemlerinde öngörülen veri hızlarına ulaşabilmek için bu sistemlerde frekans yeniden kullanım oranının 1 olmasına ihtiyaç¸ vardır, bu ise özellikle hücre sınırlarındaki kullanıcıların önemli ölçüde hücreler arası girişime maruz kalmalarına neden olur. Telsiz erişim terminalleri arasında işbirliği hücreler arası girişimin azaltılmasında önemli bir rol oynamaktadır. Bu bildiride çok hücreli, çok girdili çok çıktılı, dikgen frekans bölmeli çoklu erişim sistemlerinde telsiz erişim terminallerinden kullanıcılara işbirlikli veri iletimi problemini ele alıyoruz. Telsiz erişim terminallerinin aralarında kısıtlı ileti paylaşımı ile çizelgeleme ve veri iletimi yaptıkları etkin bir işbirlikli algoritma öneriyoruz.
Unknown
Distributed construction and maintenance of bandwidth-efficient bluetooth scatternets
(IEEE, 2005-05) Tekkalmaz, Metin; Sözer, Hasan; Körpeoǧlu, İbrahim
Bluetooth networks can be constructed as piconets or scatternets depending on the number of nodes in the network. Although piconet construction is a well-defined process specified in Bluetooth standards, scatternet construction policies and algorithms are not well specified. Among many solution proposals for this problem, only a few of them focus on efficient usage of bandwidth in the resulting scatternets. In this paper, we propose a distributed algorithm for scatternet construction problem, that dynamically constructs and maintains a scatternet based on estimated traffic flow rates between nodes. The algorithm is adaptive to changes and maintains a constructed scatternet for bandwidth-efficiency when nodes come and go or when traffic flow rates change. Based on simulations, the paper also presents the improvements in bandwidth-efficiency provided by the proposed algorithm. © 2005 IEEE.
Unknown
An efficient broadcast scheduling algorithm for pull-based mobile environments
(2000) Karakaya, K. Murat
Thanks to the advances in telecommunications and computers, today mobile computing becomes a significant means in every pace of life. Many people are now carrying portable devices such as laptop computers, Personal Digital Assistants (PDAs), and cellular phones. These mobile computing devices are supported by rapidly expanding telecommunication technology. Cellular communication, wireless LAN and WAN, and satellite services are available for daily life applications, and portable devices make use of these wireless connections to contact the information providers. Thus, a user does not need to maintain a fixed connection in the network and may enjoy almost unrestricted user mobility. As the new and various mobile infrastructures emerge, users demand a new class of applications running in this environment. However, the narrow bandwidth of the wireless communication channels, the relatively short active life of the power supplies of mobile units, and the mobility of clients make the problem of data retrieval more difficult than that in wired networks. Therefore, mechanisms to efficiently transmit information to vast numbers of mobile users are of significant interest. Data broadcasting has been considered one of the most promising ways of data dissemination in mobile environments. There are two basic data broadcasting approaches available: push and pull. In push-based broadcasting approach, data is broadcast to mobile users according to users' profiles or subscriptions, whereas in pull-based broadcasting approach, transmission of data is initiated by the explicit request of users. In this thesis, we have focused on the problem of scheduling data items to broadcast in a pull-based environment. We have developed an efficient broadcast scheduling algorithm, and comparing its performance against several well-known algorithms, we have observed that our algorithm appears to be one of the best algorithms proposed so far.
Open Access
An efficient method for generating updates in processing location dependent continuous queries
(2001-09) Yoncacı, İlker
Recent advances in wireless communication networks and portable computers have greatly increased the functionality of mobile information services and mobile computing applications. Most of those applications are expected to support location-dependent continuous queries (LDCQs) in the near future. A LDCQ is evaluated continuously in the system for a period of time and the changing results can be transmitted to the requesting client. The result of a LDCQ depends on both the locations of mobile objects on which the query has been issued and the location of the mobile client which has submitted the query. The result of a LDCQ can be provided to the requesting client as a set of tuples < S, begin, end > indicating that object S satisfies the query from time begin to time end. The correctness and timeliness of query results of LDCQs have been studied by employing an adaptive monitoring method (AMM) that manages the locations of moving objects. In this thesis, we propose a Categorized Adaptive Monitoring Method (CAMM) which allows to specify various criticality levels for LDCQs. The aim of CAMM is to provide higher levels of correctness for query results as the criticality of the query increases, without significantly increasing the wireless bandwidth requirements. We provide a simulation model with multiple criticality levels and evaluate the performance of the mobile system and the proposed method with extensive simulation experiments.
Open Access
A face tracking algorithm for user interaction in mobile devices
(IEEE, 2009-09) Bülbül, Abdullah; Çipiloğlu, Zeynep; Çapin, Tolga
A new face tracking algorithm, and a human-computer interaction technique based on this algorithm, are proposed for use on mobile devices. The face tracking algorithm considers the limitations of mobile use case - constrained computational resources and varying environmental conditions. The solution is based on color comparisons and works on images gathered from the front camera of a device. The face tracking system generates 2D face position as an output that can be used for controlling different applications. Two of such applications are also presented in this work; the first example uses face position to determine the viewpoint, and the second example enables an intuitive way of browsing large images. © 2009 IEEE.
Open Access
LineKing: Crowdsourced line wait-time estimation using smartphones
(Springer, 2013) Bulut, M. F.; Yilmaz, Y. S.; Demirbaş, M.; Ferhatosmanoğlu, N.; Ferhatosmanoğlu, Hakan
This paper describes the design, implementation and deployment of LineKing (LK), a crowdsourced line wait-time monitoring service. LK consists of a smartphone component (that provides automatic, energy-efficient, and accurate wait-time detection), and a cloud backend (that uses the collected data to provide accurate wait-time estimation). LK is used on a daily basis by hundreds of users to monitor the wait-times of a coffee shop in our university campus. The novel wait-time estimation algorithms deployed at the cloud backend provide mean absolute errors of less than 2-3 minutes. © 2013 ICST Institute for Computer Science, Social Informatics and Telecommunications Engineering.
Open Access
Novel predistortion algorithm for OFDMA
(IEEE, 2009) Ali, S.; Markarian, G.; Arıkan, Erdal
The RF amplifier in a wireless communication system is usually non-linear in nature. If such an amplifier is used in OFDMA based systems, it will cause serious degradation. This degradation will be both in terms of the reduction in BER and the generation of out of band noise. In this paper we have worked on the linearization method of the amplifier. This work is on a hybrid methodology, in which estimation of the model is performed in frequency domain and compensation is performed in time domain. The downlink preamble of the IEEE802.16e system is used here for the estimation purpose. The results for the suppression of spectra are shown at the end.
Open Access
An optimal network dimensioning and initial energy assignment minimizing the monetary cost of a heterogeneous WSN
(IEEE, 2009) Sevgi, Cüneyt; Kocyigit, A.
In this paper, a novel method is proposed to dimension a randomly deployed heterogeneous Wireless Sensor Network (WSN) of minimum monetary cost satisfying minimum coverage and minimum lifetime requirements. We consider WSNs consisting of two different types of nodes clusterheads and ordinary sensor nodes, randomly deployed over a sensing field. All devices are assumed to be stationary and have identical sensing capabilities. However, the clusterheads are more energetic and powerful in terms of processing and communication capabilities compared to sensor nodes. For such a network, finding minimum cost WSN problem is not a trivial one, since the distribution of the mixture of two different types of devices and the batteries with different initial energies in each type of device primarily determine the monetary cost of a WSN. Therefore, we formulated an optimization problem to minimize the monetary cost of a WSN for given coverage and lifetime requirements. The proposed optimization problem is solved for a certain scenario and the solution is validated by computer simulations. © 2009 IEEE.
Open Access
Processing of continuous queries from moving objects in mobile computing systems
(1999) Gök, Hüseyin Gökmen
Recent advances in computer hardware technology and wireless communication networks have led to the emergence of mobile computing systems. In a mobile computing environment, a user with a wireless connection to the information network can access data via submitting queries to the data server. Since the mobility is the most distinguishing feature of the mobile computing paradigm, location becomes an important piece of information for the so called location-dependent queries where the answer to a query depends on the current location of the user who issued the query. A location-dependent query submitted by a mobile user can become more difficult to process when it is submitted as a continuous query for which the answer changes as the user moves. The answer to a location-dependent continuous query is a set that consists of tuples < 5', begin, end > indicating that object S is the answer of the query from time begin to time end. Once the tuples in the answer set are determined, the next step is to determine when to send these tuples to the user. The transmission time of the tuples is critical in the sense that it can affect the communication overhead imposed on the wireless network and the availability of tuples in case of disconnections. In this thesis, we propose three tuple transmission approaches that determine the transmission time of a tuple in the answer set of a location-dependent continuous query. We also design and implement a simulation model to compare the performance of the proposed tuple transmission approaches under different settings of environmental parameters.
Open Access
A strong user authentication protocol for GSM
(IEEE, 2005-06) Aydemir, Özer; Selçuk, Ali Aydın
Traditionally, the authentication protocols for cellular phone networks have been designed for device authentication rather than user authentication, which brings certain limitations and restrictions on the functionality of the system. In this paper we propose a user authentication protocol for the Global Standards for Mobile (GSM) which permits the use of weak secrets (e.g. passwords or PINs) for authentication, providing new flexibilities for the GSM users. © 2005 IEEE.